IP fabric data center (DC) is an emerging technology for data center networks. Typically, an IP fabric data center uses a topology based on a two-tier fat-tree, where each leaf router connects to each spine router and vice versa. Within the fabric, an interior gateway protocol (IGP) such as IS-IS and a protocol independent multicast (PIM) (e.g., PIM-SM) are used for unicast and multicast traffic, respectively. To support interconnectivity among data centers certain leaf routers, referred to as border leafs (BLs), connect each data center to a backbone network.
To provide multitenant separation, different virtual local area networks (LANs) are created using an overlay. For example, virtual extensible local area network (VxLAN) is layer 2 overlay used to create isolated, multi-tenant logical networks that span physical network boundaries. VxLAN encapsulates customer frames with a VxLAN header and uses UDP/IP for transportation. A VxLAN header contains a VxLAN segment ID/VxLAN network identifier (VNI), which is a 24-bit field to identify a given virtual layer 2 network.
While the 24-bit field allows a large number of distinct VxLANs to coexist on a common physical infrastructure (addressing a scalability issue for conventional VLANs), VxLAN nevertheless has some scalability issues. For example, when connecting different data centers, the IP backbone network needs to maintain (S, G) multicast states proportional to the number of VxLAN Tunnel End Points (VTEPs) functioning as multicast sources. Similarly, the next hop adjacencies in VTEP tables are proportional to the number of source VTEPs. Further, virtual machine (VM) machine migration within a data center incurs MAC moves in other data centers. Given a possible large number of VTEPs, both software and hardware, and frequent VM movement within a data center, a straightforward approach for managing multicast traffic states in interconnected IP fabric data centers does not scale well.